1. Field of the Invention
The present invention relates to an aluminum nitride sintered body that is preferable as a semiconductor manufacturing apparatus member such as heater material or electrostatic chuck material.
2. Description of the Related Art
Conventionally, an aluminum nitride sintered body has superior heat resistance and corrosion resistance and has a high thermal conductivity. Thus, an aluminum nitride sintered body is used, in a semiconductor manufacturing apparatus (e.g., plasma etching apparatus, plasma CVD apparatus), as base material of an electrostatic chuck for fixing a wafer or a ceramics heater for heating a wafer. For example, a current application for an electrostatic chuck mainly uses a Johnson Rahbeck force as a chucking force. In order to obtain a favorable chucking property, this electrostatic chuck as base material requires a relatively-low volume resistivity of 108 to 1012 Ωcm. However, aluminum nitride itself is high-resistance material having a volume resistivity at a room temperature of 1014 Ωcm or more and thus must have a lower resistivity. Due to the background as described above, as disclosed in Japanese Patent No. 3457495, Japanese Laid-Open Patent Publication No. 2001-163672, Japanese Laid-Open Patent Publication No. 2003-55052, and Japanese Laid-Open Patent Publication No. 2004-262750, the applicant of the present application has developed an aluminum nitride sintered body having a low resistivity of about 108 to 1012 Ωcm by adding rare-earth oxide (e.g., yttrium oxide, cerium oxide, samarium oxide, and europium oxide) to aluminum nitride sintered body.
As described above, the base material used for an electrostatic chuck application requires a volume resistivity of about 108 to 1012 Ωcm in order to obtain a chucking force based on the Johnson Rahbeck principle. However, among ceramic members used in semiconductor-manufacturing apparatuses, there is a case where a lower resistivity is required depending on an application. For example, in a plasma etching apparatus or the like, a ring-shaped ceramic member is placed around the electrostatic chuck to prevent the base substance of the electrostatic chuck from corrosion by halide gas. An insulative ceramic has been conventionally used for this ring-shaped member.
However, to generate uniform and stable plasma on a wafer to be placed on the electrostatic chuck, it is desired to use a material having the volume resistivity equivalent to that of the wafer as the ring-shaped member which is exposed around the wafer. Accordingly, it is necessary to provide the base substance material for the ring-shaped member with electric conductivity equal to or below 104 Ωcm, which represents a semiconductor region equivalent to a silicon wafer, for example. Moreover, a ceramic member having higher electric conductivity can diversify usability not only for semiconductors but also for various applications as an electrically conductive member provided with corrosion resistance, heat resistance and strength.
For example, a method of adding an electrically conductive material such as titanium nitride (TiN) with an insulative ceramic material is known as a method of reducing a value of resistance of a ceramic. However, to obtain the volume resistivity equal to or below 104 Ωcm according to by this method, a large amount of the electrically conductive material equal to or above 20 vol % must be added because it is necessary to form electrically conductive paths inside the ceramic material by use of the electrically conductive material.
However, when such a large amount of the electrically conductive material is added, it is difficult to maintain characteristics properties of the ceramic material being a mother material. For example, when aluminum nitride is used as the mother material, there is a risk of damaging the high thermal conductivity, the heat resistance, and halogen resistance of aluminum nitride. Therefore, to maintain the characteristics properties of the mother material, it is desired to use an additive material which can reduce the value of volume resistivity by adding the material as little as possible.
The present invention has been made in order to solve the above-described disadvantages. It is an objective of the invention to provide an aluminum nitride sintered body that retains the property unique to aluminum nitride and that has a resistance controlled in a wide range.